The present invention relates to a multilayer waterproof photographic paper support of especially high surface smoothness and good photographic properties and a process for its manufacture.
Waterproof coated photographic paper supports of various designs are known. DE-AS No. 14 47 815 describes a paper support for light-sensitive coatings coated on both sides with polyolefin resin. A paper support is described in DE-OS No. 30 22 451 coated on both sides with layers of varnish hardened by electron beams. Finally, DE-OS No. 30 22 709 describes a paper carrier coated with hardenable mixtures, where a coating in contact with a profiling surface is hardened, and which as a result is characterized by high smoothness of surface. The new waterproof varnish coatings hardened by electron beams as described in DE-OS No. 30 22 451 and DE-OS No. 30 22 709 are in particular more scratch-resistant than the hitherto customery polyolefin coatings in accordance with DE-AS No. 14 47 815. The possibility of higher pigmentation is additionally provided, resulting in improved resolution of images and the improvement of the surface structure in accordance with DE-OS No. 30 22 709 contributes significantly to the fact that thinner photographic layers can be uniformly applied. This also results in an improvement of image quality.
A disadvantage of support materials with electron beam-hardened coatings has hitherto been that, with normal storage of photographic products, a minor alteration occurs in the sensitivity of photographic coatings and with more prolonged periods of storage a measurable fog. This disadvantage becomes noticeable after some months of storage.
It has hitherto been unclear why stability in storage is not assured because the starting materials have no measurable influence upon the photographic layers. It is assumed that a photochemically active low-molecular substance or impurity penetrates through diffusion into the photographic coatings and there reacts, after it first became photochemically active through radiation. Such low-molecular substances are contained in the hardenable or still unhardened layer.
In order to counter this disadvantage, the coating hardened by electron beams in accordance with DE-OS No. 30 46 130 was covered with an additional polyolefin layer. Achievement of good surface characteristics in the support storage stability of several months was, thus, successfully achieved and a product suitable for use in normal conditions obtained. However, a disadvantage after printing was a reduction in sharpness of the image occasioned by the polyolefin covering. Also noticeable as a disadvantage in this design arrangement, is the sensitivity to scratching of the polyolefin surface. The durability of the photographic material is, moreover, limited by the polyolefin which is appreciably inferior in resistance to aging relative to the traditional photo supports with barium sulfate coatings.
It is therefore an object of the present invention to create a waterproof and scratch-resistant photographic support element of great durability which not only has a stable, uniformly smooth surface, but also, after an extended period of storage, has no influence upon the sensitivity of superimposed photographic layers and does not cause disturbing fog in the photographic layers.